DA1641.004
1 February, 2019
APPLICATION INFORMATION (continued)
Figures 5 and 6 show examples of reference measurement clock signal in capacitance decrease sensing
(DSEL=GND, RCOM=1.5M, RINC=0) when clock period is calculated either using ten or twenty clock pulses
respectively.
Figure 5. TEST pin signal closer look for measuring period of ten pulses of reference measurement burst
Measured reference measurement period of ten clock pulses (N=10) is TNOSC(REF)=162.6s. Using equations 10 and
8 we can calculate clock frequency and corresponding sensor capacitance.
fREF=10/162.6s =61.5kHz, CSENSOR=1/[2*(1.5M+0)*61.5kHz]=5.42pF.
Figure 6. TEST pin signal closer look for measuring period of twenty pulses of reference measurement burst
Measured reference measurement period of twenty clock pulses (N=20) is TNOSC(REF)=310.8s. Now we get little
more precise clock frequency and sensor capacitance value.
fREF=20/310.8s =64.35kHz, CSENSOR=1/[2*(1.5M+0)*64.35kHz]=5.18pF.
10 (14)
MAS [ MICRO ANALOG SYSTEMS ]
